You must finish the game first (Kill Diablo in D2, Kill Baal in D2X), and then go back to Act I on the same difficulty level, and execute the cube recipe of Wirt’s Leg + a Town Portal Tome, while your character is standing in the Rogue Encampment.

The cow level in the final game does not take place in the Act One caves, nor are any of the cows brown in coloration, so clearly there were some changes made during development. It was taken as simply an April Fools’ Joke at the time, but the joke was clearly on us, as things turned out. The first hint of a secret cow level came on April 1, 1999, over a year before Diablo II was released, when this screenshot was released.

However, the Diablo II team apparently drew upon the rumor for inspiration and worked the whole level into Diablo II. There is no secret level or anything related to the cows other than an Easter Egg-style joke in Diablo Hellfire, and Blizzard repeatedly denied its existence in both serious and humorous ways, such as the StarCraft cheat code “there is no cow level.” There were player-created rumors/jokes about a Secret Cow Level in Diablo I, based on the cows in the pasture in Tristram that would moo, or cause your character to say something amusing, if you clicked the bovines long enough.

Diablo 2 how to open cow level